The Stable update KXDCNBF21.0 has been officially released for MI 3/4 / 4 LTE CT (codename is cancro). Before updating, please make sure you have downloaded the exact ROM matching your Xiaomi phone/tablet. In Fastboot mode, you can check model code by typing fastboot getvar product in cmd/shell.
The firmware files posted here are all official Xiaomi MIUI or HyperOS ROM, xiaomiROM.com do not own and never modified those firmwares，you will always download the file from Xiaomi server.
You may interest in those contents: MI 3/4 / 4 LTE CT ROM Topics Xiaomi Devices Index
Download Mi 3 / Mi 4 (cancro) China MIUI KXDCNBF21.0 Fastboot ROM with Android 4.4. Firmware size is 734.5 MB.